CM30 said:
Well, that's a bit of a vague question. There are easily many millions of each, so it's pretty hard to make a comparison (especially when you move into self hosted sites, like the majority of the internet).
I think blogs became less than a majority self-hosted in like 2013 or 2014 because of tumblr, and if you count Twitter and Facebook as blogging sites.
The real question at this point or even when this was posted is how much bigger than forums blogs are. You don't even need to have something to post now for a blog, since they basically do nothing but regurgitate others' content anyway.
It's also very difficult to measure (warranting a discussion a priori) because of the fact not as many people can run a forum as can run a blog, both in theory (Admins are a minority on any well-run forum.) and in practice (Not many people can run forums.), and as such users of forums are more comparable to bloggers than admins of forums who are the technical equivalent.
The easiest way to measure activity would probably be posts on tumblr minus posts on 4chan divided by two, but 4chan is barely even a forum. Perhaps Reddit would be comparable, but downvotes also provide a censorship system on Reddit, and it is really just a blog where anyone can post. On forums, on the other hand, censorship is done by ridiculing, nullifying, or opposing someone -- in other words, it is not actually censorship.
Matt implied social networks are separate, but personally say they're microblogging or status updating with comments, rather than sites like tumblr, which are blogging sites with social networking on the side. FB and Twitter probably don't count though because they are simply status update spam -- you may as well start calling G+ Communities, mailing lists, Google Groups et al, and reddit forums.
